This invention relates generally to plastic bags and, more specifically, to plastic bags having zipper openings.
Plastic bags having plastic xe2x80x9czipperxe2x80x9d openings have had enormous popularity over the last 20 years. Such plastic bags can be repeatedly sealed and resealed without the necessity of tools and without extraneous devices (such as twist ties, tape, etc.).
Rectangular-shaped plastic zipper bags are by far the most common. However, non-rectangular plastic zipper bags are also frequently used. For example, trapezoid-shaped plastic bags are considered desirable for a myriad of uses, including as storage bags in the sale of certain produce, such as grapes. In such trapezoid-shaped plastic bags, the zipper is generally disposed along the long edge of the bag.
The production line manufacture of rectangular-shaped plastic bags is simple and efficient. A zipper element is disposed along one edge of two elongate plastic sheets, the sheets are sealed on the remaining three sides and then separated from one another along the side edge seals. Because the bags are rectangular, the entirety of the two plastic sheets is readily xe2x80x9cdividablexe2x80x9d into individual bags, so this method results in no waste material.
The method, however, cannot be efficiently used in the manufacture of nonrectangular bags, such as trapezoid-shaped bags. This is because, with trapezoid-shaped plastic bags, the side of the bags carrying the zipper cannot be aligned along the single edge of an abutting pair of elongate plastic sheets without creating a large amount of waste material between the sealed short sides.
Accordingly, there is a need for a method of manufacturing non-rectangular bags, especially trapezoid-shaped bags, which avoids the above-referenced problems in the prior art.
The invention satisfies this need. The invention is a new process for manufacturing plastic bags. In the process, zippers are disposed along both opposing edges of a pair of contiguous elongate plastic sheets. The elongate plastic sheets are then divided into individual bags by sealing the two plastic sheets to one another along spaced-apart transverse sealing lines. By these steps, the pair of elongate plastic sheets are transformed into a strip of plastic bags comprising a plurality of individual plastic bags attached to one another along abutting transverse sealing lines. Each plastic bag along the strip of plastic bags has a zippered upper edge and a zippered lower edge. Next, the upper edge of every other plastic bag along the plastic bag strip is sealed with a sealing edge disposed parallel to and proximate to the zipper along the upper edge. On each of the other bags along the plastic bag strip, the lower edge is sealed with a sealing line disposed parallel to and proximate to the zipper along the lower edge. Lastly, the plastic bags are separated from one another by severing the plastic bag strip along the transverse sealing lines.
The method is especially useful in the preparation of trapezoid-shaped bags. However, the method can be easily adapted to make bags having the shape of any nonrectangular tetrahedron.